Behind the Paper - The effect of long-term exposure to microgravity on the perception of upright

Discover the story behind our paper, "The effect of long-term exposure to microgravity on the perception of upright, which was published in npj Microgravity

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Our article entitled "The effect of long-term exposure to microgravity on the perception of upright" was published in the journal npj Microgravity. The Nature Research team had a few questions for us about our article, which we have answered below.

What was the main aim of your research and why did you decide to investigate this?

Going up into space is a highly disorienting experience. My Multisensory Integration Lab at York University in Toronto, in collaboration with others at York and at MIT, has long had had an interest in what happens in microgravity. Our perception of upright is determined by a multisensory process in which information from visual cues, gravity cues and the perceived orientation of the body are combined. Visual cues include seeing the ground plane but also seeing the arrangement of objects where some lie on top of others and everything is anchored to the ground. The direction of gravity cues can be sensed by the vestibular system in the inner ear and pressure cues from the support surface. There is also a background assumption that the body is upright and that gravity is acting along its long axis. These are combined to provide the brain with the best guess about the direction of up. To investigate how this is done we can easily manipulate or remove visual cues but removing gravity can only be done using extended periods of free-fall provided by the International Space Station (ISS). The main aim of the research was to see how visual and body cues to orientation are combined in the absence of gravity.

It is important to know how this is done to tell us about how these cues are normally combined on earth and to understand the effect of losing gravity cues in clinical conditions in which there is damage to the gravity sensing organs. Our results may also be of practical use to help design countermeasures to the disorientation experienced by astronauts. Disorientation is not only unpleasant and disabling but can also represent a potential safety hazard when astronauts need to be able to orient appropriately in emergency situations.

How did you go about designing your study?

In order to measure perception of orientation we needed a test that could be performed in space. The conventional test, the subjective visual vertical, involves lining up a line with “the direction in which a ball would fall”: this was clearly not suitable for use in space! We therefore developed a new test: the Oriented Character Recognition Test (OCHART), which takes advantage of the fact that some characters, e.g., the letter p, are ambiguous. Their identity (p or d?) depends on the character’s orientation. It turns out that the orientation at which such a character is least ambiguous depends on gravity, the body and visual cues to upright. On earth the various cues to orientation (vision, gravity and the body) can be arranged to indicate different directions so that the relative contribution of each can be assessed. For example lying on ones side makes the gravity and body cues orthogonal to each other. Visual cues can be arranged to be in any direction by using a screen viewed through a circular aperture to remove other visual cue. In space only the visual cue needed to be manipulated. Therefore, all the astronauts had to do was to identify the character, presented in a range of orientations when it was presented on a range of visual backgrounds of different orientations relative to their body. In order to look at the effect of being in microgravity we measured their performance before their mission, as soon as we were able after they arrived on Station, after they had been there for a few months and when they returned. Results were compared to a control group who were measured at the same intervals on earth.

What challenges did you face?

Most of the equipment that was needed for our experiment was already available on Station in the form of the CogniHood. This is a laptop in which the screen is viewed through a circular aperture (thus removing other visual cues). All we needed was to send up the software on a DVD to run on the machine. A major unexpected challenge that we faced was that the software would not install on the CogniHood laptop! It turned out that the operating system on the laptops was not compatible with our DVD – a situation that no one at NASA or CSA had anticipated. Luckily our first astronaut subject was sympathetic to our plight and agreed to run the experiment in his personal time if we could get it installed within 12 hrs. We managed to find a work-around and with NASA’s assistance (and approval) were able to send up a modified version of the software in time.

What were the key findings from your research?

Remarkably, no changes were observed in the astronaut’s perception of the direction of up during their missions. This indicated an impressive adaptability to a microgravity environment in which the dependence on visual cues to orientation was rapidly reduced to maintain its original, on-Earth relationship to the body. However, we found that this reduced emphasis on vision persisted for up to four months after the astronauts returned to earth indicating that readjusting to Earth conditions may take longer than previously thought.

What next? What further research is needed in this area?

How to maintain orientation in the absence of gravity and to reduce space sickness, which is though to be related to this issue, remains an important research topic in the space environment. Many studies are underway to address this problem using artificial stimulation of the gravity sensing organs such as providing artificial gravity by means of a centrifuge or stimulating the vestibular organs directly with electrical current. We are concentrating next on the visual cues. In a planned series of experiments on the ISS we are looking at the possibility of stimulating the balance organs using visual cues. In a virtual reality environment, we plan to give astronauts a visually induced sense of acceleration and see whether that can be used as an alternative gravity cue.

Read the article in full

Laurence Harris

Professor, York University